Article pubs.acs.org/EF
Simultaneous Determination of Dithionate and Sulfate in Leaching Solution from SO2‑Leaching Pyrolusite by Ion Chromatography Bing Qu, Wenli Hu, Lin Deng, Weiyi Sun, Sanglan Ding, Zhiwei Gan,* and Shijun Su* College of Architecture and Environment, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China S Supporting Information *
ABSTRACT: A sensitive method for simultaneous determination of dithionate and sulfate using ion chromatography equipped with a suppressed conductivity detector was developed. The flow rate was 1.2 mL min−1, and the mobile phase contained KOH, which was gradient-generated by an automatic generator. The detection limits were 0.63 and 0.42 mg L−1 for dithionate and sulfate, respectively. The correlation coefficients of the calibration curves were greater than 0.997. The linearity ranges were 5− 200 mg L−1, and the accuracies were in the range of 99.5−111%. The proposed method was rapid, accurate, and fully validated. Finally, the method was successfully applied to the analysis of the leaching liquid and slurry by SO2-leaching pyrolusite. S2O62− using X-ray fluorescence (XRF) spectrometry. However, the method was mainly to determinate insoluble residue or dried solid. In addition, there were only a few reports regarding the detection limit of S2O62− consideration, optimal detection operation, and data analysis. Recently, Petrie et al.16,17 investigated a sensitive method to determine S2O62− and SO42− using ion chromatography (IC); indeed, this method could analyze S2O62− and SO42− in combination form. However, two or more kinds of eluents containing organic reagents and different chromatographic columns were needed for determination of S2O62− and SO42−, respectively. Despite the test time being short, there was a concern that the coeluting phenomenon was caused by SO42− interference for S2O62− determination in the case of a certain concentration ratio of the two compounds being higher than 10:1. Therefore, the aim of this study was to develop a sensitive and accurate analysis method to determine S2O62− and SO42− contents in the product by SO2-leaching pyrolusite using IC with only one elution simultaneously. Precision, accuracy, and other validation parameters were evaluated. The developed method was successfully applied for the analysis of S2O62− and SO42− in the pyrolusite slurry after the desulfurization process and metallurgy for manganese material. To our knowledge, under a test condition, this is the first report on the simultaneous determination of S2O62− and SO42− using IC.
1. INTRODUCTION Dithionate (S2O62−) is found in MnO2-leaching solution by SO2, which can form a kind of highly unstable acid (H2S2O6).1−4 In the case of heating or high concentration, the formed unstable acid could decompose into sulfuric acid and sulfur dioxide.5 However, most metal dithionate is soluble in water, and dithionate salts have better thermal stability compared to sulfite.6 Nowadays, manganese hydrometallurgy has high applicability to low-grade ore (e.g., pyrolusite; its compositions are shown in Table S1 of the Supporting Information) for industrial raw material (MnSO4), which is one of the major manganese compounds and is applied variously around the world.7 Previous studies indicated that reduction leaching of pyrolusite by SO2 had a fast reaction rate with high selectivity, which could reduce impurities in leaching liquor.8−11 Therefore, it could carry on desulfurization from coal-fired boiler flue gas (SO2) and realize the goal of green manganese metallurgy and clean production. As listed in eqs 1 and 2, MnSO4 could be directly generated by bubbling SO2 gas into pyrolusite pulp, and simultaneously, a byproduct MnS2O6 is formed.1,12 SO2 + MnO2 = MnSO4
(1)
2SO2 + MnO2 = MnS2 O6
(2)
The byproduct formed in the reaction affects the quality of the product MnSO4; hence, this kind of manganese hydrometallurgy is not widely used in industrial manufacture of manganese products. Therefore, for the application of manganese hydrometallurgy by SO2-leaching pyrolusite, it is important to accurately quantify the S2O62− level in MnSO4 products and then find out some methods to remove the impurities in the production. S 2 O 6 2− could be determined by the iodine quantity method.13−15 However, dissolved SO2 (SO2·H2O) in the S2O62− solution could affect the quantification of S2O62− obviously, resulting in low reproducibility, and the thermal decomposition step before analysis is time-consuming. Petrie et al.16 developed a sensitive method for the determination of © XXXX American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Chemicals and Reagents. The standards of Na2SO4 and Na2S2O6 were purchased from Fluka and Pfaltz and Bauer, respectively. Milli-Q water was used throughout the study. 2.2. IC. IC analysis was performed using a Dionex IC-2500 system consisting of an anion membrane regeneration electrochemical suppressor (ARSRS 300, 4 mm), an autosampler, and a thermostated column compartment coupled with an EP50 conductivity detector. Separations of SO42− and S2O62− were conducted using a Dionex IonPac AG11-HC guard column and an IonPac AS11-HC analytical Received: June 3, 2016 Revised: August 29, 2016
A
DOI: 10.1021/acs.energyfuels.6b01333 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Table 1. Recoveries of the Spiked Samplesa sample
concentration (mg L−1)
S2O62−
high recovery (%) t test low recovery (%) t test high
SO42−
recovery (%) t test low recovery (%) t test a
1
2
3
4
5
adding SMAb (mg)
18.1 119 101
18.5 120 102
19.3 120 101
19.5 119 99.5
100
1.50 56.9 111
1.81 56.8 110
1.63 56.5 109
1.56 56.3 110
50
82.3 162 99.6
82.7 163 100
83.1 164 101
81.1 161 100
80
10.5 20.7 102
10.7 21.0 103
19.9 120 100 2.77 1.63 56.6 110 2.31 82.6 163 101 2.55 10.6 21.2 106 2.78
10.6 21.0 104
10.7 21.4 107
10
Dilution factor = 10. bSMA = standard material amount.
Table 2. RSD of Determination for S2O62− and SO42− sample
mg L−1
1
2
3
4
5
RSD (%)
intraday precision
S2O62−
interday precision
SO42− S2O62−
107 19.5 4.26 105 105 18.6 4.70 16.7 5.56 199
108 19.9 4.68 106 106 19.9 5.24 16.8 5.52 199
107 19.7 4.58 107 107 20.0 4.87 16.7 6.07 206
108 19.9 4.59 107 103 19.9 4.68 16.8 5.98 199
107 20.0 4.87 106 104 19.2 4.81 16.8 5.54 233
0.51 1.01 4.81 0.79 1.51 3.10 4.66 0.33 4.67 7.11
waste liquid
SO42− S2O62− SO42−
column with a SH-H-1 sample pretreatment column (ShengHan Chromatography Technology Co., Ltd., Qingdao, China). The mobile phase was EGCII KOH. Gradient elution was carried out at a flow rate of 1.2 mL min−1, and the mobile phase concentration gradient ranged from 25 to 80 mmol L−1 to proceed comprehensive detection analysis. The current limiter was 240 mA. The column temperature was 30 °C. The injection volume was 25 μL, and injection was performed by an autosampler. 2.3. Sampling and Sample Pretreatments. The leaching liquid from the slurry leaching reaction in a 1 L jet bubbling reactor designed by our previous study was collected for the determination of S2O62− and SO42−.18 The waste liquid from the reaction of pyrolusite slurry absorbing SO2 from flue gases was also sampled to detect sulfate, sulfite, and dithionate. The collected samples were diluted by Milli-Q water first (dilution factors are shown in Tables 1 and 8), and then, the pH of the liquid was adjusted using 0.1 mol L−1 KOH to remove dissolved Mn2+ and fit the pH range of the analysis column. Subsequently, the liquid was filtered using a needle filter and a vacuum suction filter. The filtered liquid was analyzed immediately to avoid S2O62− transformation. 2.4. Method Validation. The proposed method was evaluated in terms of the limits of detection, linearity, accuracy, precision, and RSU. 2.4.1. Limits of Detection. The detection limit is an important index for evaluation of the quality analysis method. The instrumental detection limits (IDLs) were evaluated using the lowest point of the calibration (3 mg L−1) and were calculated as 3 times the signal-tonoise ratio. Method detection limits (MDLs) were estimated from the spiked leaching liquid described above at three different levels using the extrapolation method and defined as 3 times the standard deviation
determined by 10 replicates of the three kinds of standard solutions, and the results are shown in Table S2 of the Supporting Information.19 2.4.2. Linearity. The linearity of the response was investigated using external calibration, which was constructed by six points ranging from 5 to 40 mg L−1. Calibration curves were obtained from weighted (1/ x2) least-squares linear regression analysis of the data, and the results are shown in Figures S1 and S2 of the Supporting Information. 2.4.3. Accuracy. The accuracy of the method was evaluated through recovery experiments. The samples were spiked with the analytes at two different concentrations (Table 1). Recoveries were calculated according to the recommendations of INMETRO.20 Gonzaáes et al.21 suggested that accuracy could be obtained by recovery experiments using standard solutions, and the mean recovery can be evaluated by the significance test (t test). Therefore, the t test was applied at a 95% confidence level. The results of the recovery experiments at two concentration levels (n = 5 for each concentration level) are given in Table 1. 2.4.4. Precision. The precision was evaluated according to the repeatability and was expressed as the relative standard deviation (RSD).22 The retention time (tR) and the measured value were studied to evaluate the repeatability. Three different concentrations of standard solutions containing SO42− and S2O62− were analyzed for five injections in 1 day and in 5 consecutive days using IC. The mean values obtained for the tR and the concentrations as well as their RSD values are shown in Table 2. All of the formulas and the calculation processes as well as the related data used in this study are shown in the Supporting Information.23 2.4.5. Uncertainty. The uncertainty degree reflects the accuracy of determination results; therefore, it is an important indicator for the B
DOI: 10.1021/acs.energyfuels.6b01333 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels result of the experiment for the recognition and measurement certification. The relative standard uncertainty (RSU) of the standard material resulted from three parts, including the uncertainty of the processes of the standard material, the uncertainty of the standard material inhomogeneity, and the uncertainty of the instability of the standard material. The uniformity and stability of dithionate material are satisfactory, and thus, the corresponding parts of the uncertainty could be ignored.24,25
3. RESULTS AND DISCUSSION 3.1. Optimization of IC for the Analysis of S2O62−. IC retentions, including retention time, flow rate, and retention volume, are the most important thermodynamic parameters for chromatographic qualitative analysis and quantification. 3.1.1. Eluent Concentration. The gradient elution method was employed to ensure high resolution and appropriate retention time for dithionate analysis.26 As seen in Figure 1, the
Figure 2. Analysis of the blank solution (from left to right: Cl−, NO3−, SO42−, and CO32−).
Figure 1. Influence of the eluent concentration on the retention time of S2O62−.
Figure 3. Influence of the eluent flow rate on the retention time of S2O62−.
eluent concentration significantly influenced the analysis of S2O62− and S2O62− was detected in the case of the eluent concentration greater than 50 mmol L−1. The retention time of S2O62− decreased with an increasing eluent concentration; however, the eluent concentration was limited by the flow rate (13.6−83.3 mmol L−1, while the flow rate was 1.2 mL min−1). Therefore, 80 mmol L−1 was chosen to achieve rapid analysis and a symmetrical peak. For SO42− analysis, to separate SO42− from interfering anions, such as NO3− and CO32−, which existed in the water used in the pyrolusite slurry (the anion compositions of water are shown in Figure 2), 25 mmol L−1 initial eluent concentration was selected to achieve shortening of the detection time and elimination of interference from neighboring peaks and to ensure separation degree R ≥ 2.0.27 Therefore, gradient elution from 25 to 80 mmol L−1 to detect S2O62− and SO42− simultaneously was chosen to control a stable retention time in about 28 min and catch good peak symmetry. 3.1.2. Flow Rate. As shown in Figure 3 and Table 3, the flow rate influenced the accuracy significantly as well as tR. A higher flow rate resulted in a higher pressure and shorter retention time but also caused a higher deviation. The accuracy of the measurement decreased with an increasing flow rate; therefore, a flow rate of 1.2 mL min−1 was chosen to achieve accurate
analysis of S2O62− and SO42−. Under the flow rate of 1.2 mL min−1, the retention time was stable and the baseline was smooth. 3.2. Limit of Detection. For S2O62−, the IDL was 0.63 mg L−1 and the MDL was 1.35 mg L−1, while for SO42−, the IDL was 0.42 mg L−1 and the MDL was 0.92 mg L−1. The matrices in the leaching liquid might suppress the responses of S2O62− during sample analysis.
4. LINEARITY The calibration curves are shown in Figures S1 and S2 of the Supporting Information. The correlation coefficients of the two calibrations were better than 0.997. However, when the S2O62− concentration was higher than 150 mg L−1, the measured value was 1.15 times the nominal value and As (As is the ratio of the peak width and shown in the Supporting Information) was more than 1.7. At the same time, the tail peak was obtained; hence, the linearity range up to 70 mg L−1 for determination of S2O62− was suggested. 5. INTERFERENCE 5.1. Interfering Peak. The strong retention substance, such as S2O62−, could be separated well from the matrix as a result of C
DOI: 10.1021/acs.energyfuels.6b01333 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Table 3. Influence of the Eluent Flow Rate on IC Analysis velocity (mL min−1)
0.85
1.0
1.2
1.5
2.0
nominal value
pressure (psi) measured value of S2O62− (mg L−1) measured value of SO42− (mg L−1)
714 27.4 19.4
887 26.0 16.7
1179 21.7 13.8
1654 16.7 11.0
2244 12.2 8.79
22.3 13.0
tion process, and reproducibility of IC analysis.29 The results are shown in Table 6.
its longer retention time. The ionizing substance whose pKa was higher than 7.0 did not affect the determination, indicating no interference from common inorganic anions.28 Therefore, the developed method could be used for determination of SO42− and S2O62− simultaneously, and the retention times for each anion are shown in Table 4.
Table 6. Data for Calculation of UA (mg L−1) serial number S2O62−
Table 4. tR of the Investigated Anions (min) anion
F−
Cl−
NO3−
SO32−
SO42−
S2O62−
tR
2.93
4.18
4.71
5.15
6.05
24.7
5.2. Influence of the pH Value. The initial pH of the selected reaction liquids was less than 2.5; therefore, the pH value must be adjusted before IC analysis as a result of the pH requirement of the IC column of between 5.4 and 10.5 and to remove dissolved Mn2+. As seen from Table 5, the measured result deviations were small in acidic, neutral, and alkaline, which were less than Table 5. Influence of the pH Value on the Analysis of S2O6 and SO42− (mg L−1) ion pH
5.5
7.1
10.3
nominal value
S2O62− SO42−
49.6 11.3
49.2 10.9
49.0 10.6
49.2 11.0
1
2
3
4
5
18.6 19.2 19.5 19.8 17.8
18.4 18.8 19.9 19.8 18.3
19.0 19.2 19.7 19.3 18.8
19.1 20.3 19.9 19.4 19.1
18.6 20.0 20.0 19.9 19.2
mean value
s
19.3
0.63
UA was calculated by a total of 25 replicates in five groups and was expressed as the mean value and standard deviation. As a result of n being greater than 10, the outlier data can be found by the 3δ principle30 standard uncertainty UA = s / n = 0.63/ 25 = 0.126
2−
S2O62−
(3)
standard uncertainty
Us = U /M = 0.126/160 = 0.0008
(4)
where s is the standard deviation, n is the amount, and M is the molecular weight. The values of UA were small based on the current study, suggesting high reproducibility of the developed method. 8.2. Relative Uncertainty (RU) Introduced into the Measurement Process as Type B Uncertainty (UB). 8.2.1. RU Introduced into the Standard Stock Solution Preparation Process U1r. In the process of standard stock solution preparation, RU was introduced
0.38%. Because of the tiny effect of pH on the determination, the test method exhibits a wide application scope.
6. ACCURACY The accuracy was expressed as recovery in this study, and the results are shown in Table 1. Briefly, it was obvious that the critical t value (2.015; n = 5) was smaller than the calculated T, suggesting that the proposed determination method presented satisfactory accuracy. The recoveries of S2O62− varied from 99.5 to 111%, indicating that the extraction of the analytes was good enough to be used for the determination of the studied anions in the leaching liquid.
U1r = (Ur0 2 + Ur12 + Ur2 2)1/2 = (0.00012 + 0.00032 + 0.00062)1/2 = 0.0007
(5)
U1r is derived from the instrument error, which reflects the accuracy of the instrument.31 The smaller the value, the higher the degree of accuracy and index values. 8.2.2. RU Introduced into a Series of the Standard Solution Preparation Process U2r. The RSU of the standard solution was introduced into the preparation process.
7. PRECISION Intra- and interday precisions for the analysis of dithionate were determined by five consecutive injections of the spiked leaching agents at three different concentrations in 1 day and in 5 successive days and were expressed as the RSD of the analytical data. The results are shown in Table 2. It could be concluded that the method presented good repeatability because the observed RSD was below 10% for both intra- and interday precisions. The higher RSD of the interday precision might be due to the slow degradation of S2O62−.
U2r =
∑ ur 2 = (0.00462 + 0.00332 + 0.02412 + 0.00062 1/2
+ 0.00432 + 0.00362) = 0.0254
(6)
U2r was used to evaluate the influence of the experimental environment, e.g., environment temperature, human factors, and statistical methods.31 The estimated U2r value was small in this study, implying that the experimental environment had little influence on the experimental results (as shown in Tables S3 and S4 of the Supporting Information). 8.2.3. RU Introduced into the Least-Squares Fitting Standard Working Curve U3r. Six different levels of standard solutions (5, 10, 15, 20, 30, and 40 mg L−1) were employed,
8. UNCERTAINTY OF DETECTION 8.1. RSU of Repeatability of Sample Determination as Type A Uncertainty (UA). UA could reflect the repeatability of sample analysis, repeatability of the standard sample preparaD
DOI: 10.1021/acs.energyfuels.6b01333 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels
given in Table 8. In addition, a total of three samples, including the leaching liquid (containing Fe3+ and excluding Fe3+) and waste liquid, was also detected by IC, and the results are shown in Figure 4.
and each concentration was measured 5 times. The results are shown in Table 7. Table 7. RSU Introduced into the Standard Working Curve (mg L−1) measured value concentration
1
2
3
4
5
mean value
5 10 15 20 30 40
4.53 10.1 14.9 20.5 29.4 40.4
4.56 10.1 14.1 19.9 29.9 39.2
4.57 9.54 14.9 20.0 30.2 39.3
4.95 9.44 14.8 18.3 30.0 40.1
4.51 9.60 15.0 19.2 29.6 38.9
4.62 9.76 14.7 19.6 29.8 39.6
The U3r value was 0.33, and the calculation methods were listed in the Supporting Information. U3r is the largest source of the RSU in the determination, and a small value of U3r indicated good linearity of the calibration curve.32 8.3. Synthetic Evaluation of Uncertainty. The type A and B uncertainty components are independent; therefore, if ρij = 0, the synthetic RU is only related to uncertainty of type A and B and was calculated as listed below. Ut = ( ∑ UA 2 +
Figure 4. Chromatogram of the leaching liquid and waste liquid.
As seen in Table 8, all of the slurry samples and the semifinished product contained S2O62−, with the concentrations ranging from 4.52 to 37.3 g L−1. It should be noticed that SO42− and S2O62− have relatively stable retention times and the RSDs were 7.11 and 4.67%, respectively, in the leaching liquid samples (Figure 4 and Table 2), indicating that the developed method could be applicable to real samples. Furthermore, the S2O62− content of the sample with Fe3+ was higher than those without Fe3+ in the leaching liquid, suggesting that dithionate might be generated in the presence of Fe3+.34,35
∑ UB2 + 2 ∑ ρij δiδj)1/2
= (Us 2 + U1r 2 + U2r 2 + U3r 2)1/2 = (0.00082 + 0.00072 + 0.02542 + 0.3302)1/2 = 0.33 (7)
Ut is calculated using variance and covariance of all of the data from type A and B and estimates the standard deviation of measurement results. In this study, the Ut value was 0.33, indicating that the sensibility of the developed method was high. 8.4. Determination of Expanded Uncertainty. On the basis of the normal distribution, the optimal interval was taken as the confidence level of 0.95; therefore, coverage factor k = 2. Uy = kUt = 2 × 0.33 = 0.66
10. CONCLUSION A sensitive method for simultaneous determination of S2O62− and SO42− by suppressed conductivity IC was developed. A gradient elution was carried out at a flow rate of 1.2 mL min−1. The mobile phase was KOH, and the gradient was ramped linearly from 25 to 80 mmol L−1. The method was fully validated and exhibited satisfactory linearity, accuracy, and precision. The proposed method was successfully applied to the determination of S2O62− and SO42− in the slurry and leaching liquid samples.
(8)
Uy is used to determine the range of measurement results, and the measured value is closer to the true value when the confidence level is higher.31,33 In this study, the average level of S2O62− in the leaching liquid was 19.3 mg L−1 and was determined using the method described above by 25 replicates. The expanded uncertainty was calculated using the equation listed below. M = M̅ ± Uy = 19.3 ± 0.66 (mg L−1)
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.6b01333. Composition of pyrolusite (Table S1), results of the spiked samples for determination of the MDLs (Table S2), sampling instrument error coefficient introduced into the RU (Table S3), temperature introduced into the
(9)
9. APPLICATION OF THE METHOD The slurry (samples were collected from the surface, central, and bottom layers of the slurry) and semi-finished products were analyzed using the developed method, and the results are
Table 8. Application of the Developed Method in Waste Liquid (g L−1)a sample location 2−
SO4 S2O62− a
surface 190 5.37
central 169 4.52
206 6.07
s-mpb
bottom 199 5.98
233 6.74
188 5.54
272 37.3
Dilution factor = 20. bs-mp = semi-manufactured product. E
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RU (Table S4), curve of SO42− (Figure S1), curve of S2O62− (low concentration) (Figure S2-1), curve of S2O62− (high concentration) (Figure S2-2), and equations (PDF)
(16) Petrie, L. M.; Jakel, M. E.; Brandvig, R. L.; Kroening, J. G. Ion Chromatography of Sulfur Dioxide, Sulfate Ion, and Dithionate Ion in Aqueous Mineral Leachates. Anal. Chem. 1993, 65 (7), 952−955. (17) Petrie, L. M. Molecular interpretation for SO2 dissolution kinetics of pyrolusite. Manganite and hematite. Appl. Geochem. 1995, 10 (3), 253−267. (18) Su, S.; Zhu, X.; Liu, Y.; Jiang, W.; Jin, Y. A Pilot-Scale Jet Bubbling Reactor for Wet Flue Gas Desulfurization with Pyrolusite. J. Environ. Sci. 2005, 17 (5), 827−831. (19) Yi, G. Y.; He, W. Bias analysis and the simulation-extrapolation method for survival data with covariate measurement error under parametric proportional odds models. Biom. J. 2012, 54 (3), 343−360. (20) Instituto Nacional de Metrologia Normalizaçaõ e Qualidade Industrial (INMETRO). Orientação sobre Validação de Métodos ́ Analiticos; INMETRO: Brazil, 2010; STAN.DOQ-CGCRE-008. (21) González, A. G.; Herrador, M. A.; Asuero, A. G. Intra-laboratory testing of method accuracy from recovery assays. Talanta 1999, 48, 729−736. (22) Zhu, Y.; Zhang, F.; Tong, C.; Liu, W. Determination of glyphosate by ion chromatography. J. Chromatogr A 1999, 850, 297− 301. (23) Hao, Y. Application Examples for Measurement Uncertainty on Chemical Analysis; China Standard Press: Beijing, China, 2011; pp 3− 23, 42−58. (24) Back, A. E.; Ravitz, S. F.; Tame, K. E. Formation of Dithonate and Sulfate in the Oxidation of Sulfur Dioxide by Manganese Dioxide and Air; Bureau of Mines, United States Department of the Interior: Washington, D.C., 1952; Report of Investigations 4931, pp 5702. (25) Ward, C. B. Improved hydrometallurgical processing of manganese containing meterials. WO Patent 2005012582 A1, Feb 10, 2005. (26) Snyder, L. R.; Kirkland, J. J.; Glajch, J. L. Practical HPLC Method Development; Science Press: Beijing, China, 1998; pp 151−176, 189. (27) Hoffman, D.; Kringle, R.; Singer, J.; McDougall, S. Statistical methods for assessing long-term analyte stability in biological matrices. J. Chromatogr. B: Anal. Technol. Biomed. Life Sci. 2009, 877, 2262− 2269. (28) Silveira, E. L. C.; de Caland, L. B.; Tubino, M. Simultaneous quantitative analysis of the acetate, formate, chloride, phosphate and sulfate anions in biodiesel by ion chromatography. Fuel 2014, 124, 97−101. (29) ISO/TAG4/WG3. Guide to the Expression of Uncertainty in Measurement; International Organization for Standardization (ISO): Geneva, Switzerland, 1991, 1992. (30) Liu, S.; Zhang, X.; Wang, Y. Application of SPC 3σ Principle to Output Moisture Content Monitoring in Cut Tobacco Drying. Tob. Sci. Technol. 2010, 9, 15−17 (in Chinese). (31) Liu, Z.; Chen, K. Handbook for Measurement Uncertainty; China Metrology Press: Beijing, China, 1997; pp 55−67, 88−105. (32) Ni, Y. Evaluation of Practical Measurement Uncertainty; China Quality Inspection Press: Beijing, China, 2014; pp 22−35. (33) Bruzzoniti, M. C.; De Carlo, R. M.; Sarzanini, C. Determination of sulfonic acids and alkylsulfates by ion chromatography in water. Talanta 2008, 75 (3), 734−739. (34) Brandt, C.; Van Eldik, R. The Formation of Dithionate during the Iron(III)-Catalysed Autoxidation of Sulfer(IV)-Oxides. Atmos. Environ. 1997, 31 (24), 4247−4249. (35) Podkrajšek, B.; Grgić, I.; Turšič, J. Determination of sulfur oxides formed during the S(IV) oxidation in the presence of iron. Chemosphere 2002, 49 (3), 271−277.
AUTHOR INFORMATION
Corresponding Authors
*Telephone/Fax: +86-28-85460916. E-mail: ganzhiwei.nk@ gmail.com. *Telephone/Fax: +86-28-85460916. E-mail: sushijunscu@qq. com. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The project was supported by the National Natural Science Foundation of China (NSFC-51374150 and NSFC-51304140) and the Science and Technology Plan Projects of Sichuan Province, China (Grants 2014SZ0146 and 2015HH0067).
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REFERENCES
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DOI: 10.1021/acs.energyfuels.6b01333 Energy Fuels XXXX, XXX, XXX−XXX
